In conventional dividers, a reciprocating knife and ram acting like a large pump slides back and forth in a dough box. The dough box is fed from an overhead hopper and is connected to either a reciprocating, or a rotating or oscillating, division box. In operation the flow of dough under the force of gravity into the dough box is assisted by the suction created as the knife and ram slide backwards to uncover the transfer passage from the hopper and the dough is then forced into the division box by the ram as it moves forward with the knife, which leads the ram, such as to move through the dough stream in the transfer passage to separate and seal the dough in the dough box from the dough in the transfer passage from the hopper, and is followed by the ram which forces the dough into the division box.
The accuracy of such conventional types of dough dividers is greatly dependant on maintaining small clearances between the knife, ram and dough box, in order to obtain sufficient suction to draw the required amount of dough into the dough box. The clearances should be sufficient to allow for free relative movement between the parts, but not enough to allow the ingress of air. However, as the machine wears, the clearances increase allowing for the ingress of air and a decrease in the scaling or dividing accuracy, and because of the relatively strict regulations controlling the weight of bread, the divider is no longer commercially acceptable and the dividing head must be replaced or reconditioned or some form of compensation made by the baker. Commonly edible oil is applied to the clearances to restrict air ingress but such application of oil is of reducing effectiveness as wear increases.
It is known in order to overcome the above problem that positive pressure dividers in which continuously running disced rollers at the base of the hopper serve to draw dough from the hopper and positively force it through the transfer passage into the dough box thus avoiding the necessity for dough to be drawn or sucked into the dough box with the attendant possibility of ingress of air as with the conventional dividers referred to above. Furthermore, normal wear with a positive pressure type divider has little or no effect on the scaling or dividing accuracy. The positive pressure is imparted to the dough by means of the continuous running disc rollers by the viscous shearing forces originating on the enlarged surface of the rollers provided by the presence of the discs. The severe working of the dough by these disc rollers, also involves a cutting and tearing action which, when combined with the rather tortuous route from the feed rolls to the division box in a positive pressure divider, can be disadvantageous, in that, although a uniformly scaled product can be produced, the resulting damage to the dough structure seriously reduces the gas retaining properties of the dough and the volume of the resulting loaves after baking and hence their acceptability.
Many alternative methods of providing positive pressure have been attempted, such as the use of positive displacement pumps of varying types, but all have involved severe working and/or tearing of the dough which has in turn resulted in unsatisfactory bread being produced.
It has been determined (see article entitled "Dough Development for Shorter Bread Making Processes" by K. H. Tipples and R. H. Kilborn, October 1974 Edition of the Bakers' Digest) that working or extending of dough between rolls (called sheeting rolls) can be very effective in achieving dough development in the formation of a two dimensional highly oriented dough structure capable of a high degree of gas retention and from which bread of optimum loaf quality and volume may be obtained. The action of the rolls is to produce gentle viscous shearing within the dough mass. We have found that, if a pair of such sheeting rolls is used to impart pressure on a dough mass such that the shearing stresses created by the increasing pressure gradient are not excessive when compared with the gentle shearing stresses imposed by the extending action of the sheeting rolls, then positive pressure may be obtained without the dough damage created by disc feed rolls or other positive pumping means. Such a condition is obtained by using rolls of large diameter. With large diameter rolls the surface area in the vicinity of the narrow passage between adjacent rolls is proportionally increased and the shearing forces necessary to resist the reverse dough flow down the pressure gradient are spread over a larger area resulting in reduced shearing stresses within the dough mass and the substantial elimination of dough damage and its deleterious effect on gas retention.